1. Field of the Invention
This invention relates to a developing device used in an image forming apparatus of the electrophotographic type or the electrostatic recording type to develop an electrostatic image on an image bearing member by the use of a magnetic developer.
2. Related Background Art
Certain image forming apparatus for forming an image by an electrophotographic recording method or the like, employ a process cartridge system in which an electrophotographic photosensitive member, which is an image bearing member, and process means acting on the electrophotographic photosensitive member are integrally made into a cartridge, and this cartridge is designed to be removably mountable on an image forming apparatus body.
According to this process cartridge system, by the process cartridge being interchanged, the maintenance of the main members of the apparatus can be performed by a user himself without resorting to a serviceman and therefore, the operability of the apparatus can be markedly improved. Therefore, this process cartridge system is widely used in image forming apparatuses such as printers.
In a developing device which is developing means contained in such a process cartridge, seal members for preventing a developer from flowing out of a developing area are provided on the opposite end portions of a developing sleeve, which is a developer image bearing member that is rotated while carrying the developer thereon and can convey the developer to the developing area for developing an electrostatic latent image.
An elastic material such as felt or formed rubber is widely utilized for the seal members for preventing the outflow of the developer. In FIGS. 12 and 13 of the accompanying drawings, there is shown a case of an example in which a seal member is used. FIG. 12 is a front view showing the essential portions of a developing device contained in a process cartridge according to the prior art, and FIG. 13 is a side view showing the essential portions of the developing device.
As shown in FIG. 12, a developing sleeve 31 carrying a developer thereon has a magnet roller 32 disposed therein. Also, as shown in FIG. 13, the developing sleeve 31 is rotatably supported by a developing container 30 through a sleeve bearing 35 provided at a predetermined location on the developing container 30 containing a developer therein, and the developer supplied from the developing container 30 may adhere to the surface of the developing sleeve 31 by the magnetic force of the magnet roller 32, and the thickness of the developer layer may be regulated to a predetermined thickness by a developing blade 33 bearing against the developing sleeve 31. Thereafter, the developer may be conveyed to a developing area which is a position opposed to a latent image on a photosensitive drum disposed at a location opposed to the developing sleeve 31 with the rotation of the developing sleeve 31, and the developer conveyed to the developing sleeve may adhere to the latent image, whereby developing may be effected.
Also, an elastic seal member 36 is mounted on the developing container 30 side of the developing sleeve 31 mounted on the developing container 30 at lengthwise opposite ends outside the developing area of the developing sleeve 31. This elastic seal member 36 is formed into a substantially arcuate cross-sectional shape along the outer peripheral surface of the developing sleeve 31, for example, by felt, formed rubber or the like, and the elastic seal member 36 is brought into pressure contact with the outer peripheral surface of the developing sleeve 31 to thereby prevent the developer from flowing from the surface of the developing sleeve 31 to the lengthwise end portion thereof.
In a developing device using the elastic seal member of the above-described construction, the elastic seal member 36 is in pressure contact with substantially a half of the outer peripheral surface of the opposite end portions of the developing sleeve 31. So, this has led to a problem that the load of the developing sleeve 31 rotated during the developing operation and the elastic seal member 36 is deteriorated by its contact with the developing sleeve 31, and there is another problem that the toner, though slightly, enters from the gap between the developing sleeve 31 and the elastic seal member 36. These problems have caused torque to become high and the fluctuation of the torque has become so great to cause the irregularity of rotation, and this has adversely affected image formation.
Therefore, to solve these problems, there has been proposed a method of disposing, instead of elastic seal members, magnet seal members at predetermined intervals along the outer peripheral surface of the opposite end portions of the developing sleeve at the locations on the developing sleeve at which the elastic seal members are provided, to thereby prevent the outflow of the developer.
FIG. 14 of the accompanying drawings shows a front view of a developing device using magnet seal members. Each of the magnet seal members 37 provided at the opposite ends of a developing sleeve 31 is a magnet formed into a substantially arcuate cross-sectional shape along the outer periphery of the developing sleeve 31, and has many N and S poles magnetized on the inner peripheral surface thereof. Also, the magnet seal members 37 are disposed with a predetermined gap g relative to the outer peripheral surface of the developing container side at the opposite end portions of the developing sleeve 31 having a magnet roller 32 therein, and is mounted on the developing container with the developing sleeve 31 while keeping the gap g. The magnet seal members 37 have magnetic poles provided on the inner peripheral surfaces thereof at locations opposed to the magnetic poles of the magnet roller.
These magnet seal members 37 restrain a developer between the end portions of the developing sleeve and the magnet seal member by a magnetic field formed by the magnet roller 32 in the developing sleeve 31 and the magnet seal members 37 to form a seal portion. And the developer which has moved to the lengthwise end portion of the developing sleeve can be checked by the seal portion to thereby prevent the outflow of the developer from the end portions of the developing sleeve.
When the above-described magnet seals are used, the developing sleeve and the magnet seal members are kept in non-contact with each other and the rotational torque of the developing sleeve becomes remarkably small and therefore, a driving motor may be a compact and inexpensive one. Also, the fluctuation of the rotational torque is small and it becomes difficult for the irregularity of the rotation of the developing sleeve and the photosensitive drum to occur and there is not the wear or the like of the magnet seal members and therefore, the use thereof is semipermanent and the recycling thereof can also be coped with.
However, when the above-described magnet seal member according to the prior art is used, sufficient consideration is not given to the relations in magnetic-flux density and magnetic force between the fixed magnet in the developing sleeve and the magnet seal members and therefore, there has been the problem that depending on the situation of use, the developer may leak from the end portions of the developing sleeve.
For example, during the use of the developing device, the developer carried on the developing sleeve moves a great deal to the lengthwise end portions of the developing sleeve with the rotation of the developing sleeve, and this has led to the problem that the developer, which has thus moved, slips through the seal portions formed between the end portions of the developing sleeve and the magnet seal members.